SELECTIVE ROBUST HEADER COMPRESSION (RoHC) FOR A VoIP CALL IN A CELLULAR COMMUNICATIONS NETWORK

ABSTRACT

Systems and methods for selectively enabling Robust Header Compression (RoHC) for Voice over Internet Protocol (VoIP) calls in a cellular communications network are disclosed. In one embodiment, a data radio bearer for a VoIP call is established between a base station and a mobile terminal. During the VoIP call, a radio frequency parameter for the data radio bearer is monitored. When the radio frequency parameter for the data radio bearer satisfies a predefined coverage-based condition, the base station enables RoHC for the VoIP call. In one preferred embodiment, the radio frequency parameter is a Signal-to-Interference-plus-Noise Ratio (SINR) for the data radio bearer for the VoIP call, and the predefined coverage-based condition is a predefined SINR threshold below which the base station enables RoHC. By enabling RoHC in this manner, RoHC resources are selectively made available for those VoIP calls that will benefit most from increased cell coverage provided by RoHC.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to Voice over Internet Protocol(VoIP) calls in a cellular communications network and more particularlyrelates to Robust Header Compression (RoHC) for VoIP calls in a cellularcommunications network.

BACKGROUND

Voice over data networks has been seen as the next step in the evolutionof wireless voice in cellular communications networks. The preferredprotocol for enabling this evolution is Voice over Internet Protocol(VoIP). When using VoIP, each voice frame is routed using an InternetProtocol (IP) header. The IP header for VoIP is considerably larger thanthe very small header used for transporting voice traffic over the airin traditional 2G/3G cellular communications networks. This implies thatthe header overhead to payload ratio when using VoIP is much larger thanthat in traditional 2G/3G cellular communications networks, which isundesirable. One solution to this problem is the use of Robust HeaderCompression (RoHC) to compress the IP header before the IP header istransmitted over the air.

One key benefit of RoHC when used with VoIP in Long Term Evolution (LTE)cellular communications networks is improved cell coverage for VoIPusers. In particular, RoHC decreases the number of bits needed per VoIPpacket, thus decreasing the risk that VoIP packet segmentation willoccur. This translates into a path-loss improvement, which in turnincreases the cell coverage for the VoIP user.

RoHC is a resource intensive application. In other words, RoHC requiresa significant amount of resources (i.e., processing cycles and memory)at a base station in a cellular communications network. One issue thatarises when using RoHC with VoIP is that the base station may not havesufficient resources to enable RoHC for all VoIP calls. As such, thereis a need for systems and methods that selectively enable RoHC for VoIPcalls in a cellular communications network.

SUMMARY

The present disclosure relates to systems and methods for selectivelyenabling Robust Header Compression (RoHC) for Voice over InternetProtocol (VoIP) calls in a cellular communications network. In oneembodiment, a data radio bearer for a VoIP call is established between abase station and a mobile terminal. During the VoIP call, a radiofrequency parameter for the data radio bearer is monitored. When theradio frequency parameter for the data radio bearer satisfies apredefined coverage-based condition, the base station enables RoHC forthe VoIP call. In one preferred embodiment, the radio frequencyparameter is a Signal-to-Interference-plus-Noise Ratio (SINR) for thedata radio bearer for the VoIP call, and the predefined coverage-basedcondition is a predefined SINR threshold below which the base stationenables RoHC. Still further, in one particular embodiment, thepredefined SINR threshold is a predefined SINR threshold below which thebase station enables Transmit Time Interval (TTI) bundling. By enablingRoHC in this manner, RoHC resources are selectively made available forthose VoIP calls that will benefit most from increased cell coverageprovided by RoHC.

In one embodiment, a base station has a finite amount of RoHC resources(i.e., processor cycles and memory resources) that are available forRoHC. The RoHC resources are logically divided into a first-come,first-serve RoHC resource pool and a selective RoHC resource pool. Adata radio bearer for a VoIP call is established between the basestation and a mobile terminal. During the VoIP call, a radio frequencyparameter for the data radio bearer is monitored. When the radiofrequency parameter for the data radio bearer satisfies a predefinedcoverage-based condition, the base station performs a selective RoHCadmission process. In one preferred embodiment, the radio frequencyparameter is a SINR for the data radio bearer for the VoIP call, and thepredefined coverage-based condition is a predefined SINR threshold belowwhich the base station enables RoHC. Still further, in one particularembodiment, the predefined SINR threshold is a predefined SINR thresholdbelow which the base station enables TTI bundling. As a result of theselective RoHC admission process, the base station enables RoHC for theVoIP call if there are available RoHC resources in either thefirst-come, first-serve RoHC resource pool or the selective RoHCresource pool. Conversely, if there are no available RoHC resources inthe first-come, first-serve RoHC resource pool and the selective RoHCresource pool, the base station does not enable RoHC for the VoIP call.

In another embodiment, a data radio bearer for a VoIP call isestablished between the base station and a mobile terminal. During theVoIP call, a SINR for the data radio bearer is monitored. When the SINRfor the data radio bearer falls below a predefined threshold fortriggering TTI bundling, the base station performs an intra-cellhandover procedure to establish a new data radio bearer for the VoIPcall in which both TTI bundling and RoHC are enabled.

In yet another embodiment, a base station has a finite amount of RoHCresources (i.e., processor cycles and memory resources) that areavailable for RoHC. The RoHC resources are logically divided into afirst-come, first-serve RoHC resource pool and a selective RoHC resourcepool. A data radio bearer for a VoIP call is established between thebase station and a mobile terminal. During the VoIP call, a SINR for thedata radio bearer is monitored. When the SINR for the data radio bearerfalls below a predefined threshold for triggering TTI bundling, the basestation performs a selective RoHC admission process. As a result of theselective RoHC admission process, the base station determines that RoHCis to be enabled for the VoIP call if there are available RoHC resourcesin either the first-come, first-serve RoHC resource pool or theselective RoHC resource pool. Conversely, if there are no available RoHCresources in the first-come, first-serve RoHC resource pool and theselective RoHC resource pool, the base station determines that RoHC isnot to be enabled for the VoIP call. The base station then performs anintra-cell handover procedure to establish a new data radio bearer forthe VoIP call in which TTI bundling is enabled and RoHC is enabled ordisabled according to the result of the selective RoHC admissionprocess.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 illustrates a cellular communications network providing selectiveRobust Header Compression (RoHC) for Voice over Internet Protocol (VoIP)calls according to one embodiment of the present disclosure;

FIG. 2 is a flow chart that illustrates the operation of a base stationto selectively enable RoHC for a VoIP call according to one embodimentof the present disclosure;

FIGS. 3A and 3B graphically illustrate a Hybrid Automatic Repeat Request(HARQ) transmission scheme without and with Transmit Time Interval (TTI)bundling;

FIG. 4 illustrates the operation of a base station to perform anintra-cell handover to enable both TTI bundling and RoHC for a VoIP callaccording to one embodiment of the present disclosure;

FIG. 5 is a flow chart that illustrates the operation of a base stationto selectively enable RoHC for a VoIP call according to anotherembodiment of the present disclosure;

FIG. 6 is a block diagram of a base station according to one embodimentof the present disclosure; and

FIG. 7 is a block diagram of a mobile terminal according to oneembodiment of the present disclosure.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

The present disclosure relates to systems and methods for selective

Robust Header Compression (RoHC) for Voice over Internet Protocol (VoIP)calls in a cellular communications network. Notably, much of thediscussion herein focuses on selective RoHC for VoIP calls in a LongTerm Evolution (LTE) cellular communications network. As such, LTEterminology is oftentimes used throughout this disclosure. However, theconcepts disclosed herein are not limited to LTE cellular communicationsnetworks. Rather, the concepts disclosed herein may be used to provideselective RoHC for VoIP calls in other types of cellular communicationsnetworks.

FIG. 1 illustrates a cellular communications network 10 that providesselective RoHC for VoIP calls according to one embodiment of the presentdisclosure. In this embodiment, the cellular communications network 10is a LTE cellular communications network. However, as discussed above,the present disclosure is not limited thereto. The cellularcommunications network 10 includes a number of cells 12-1 through 12-19,which are generally referred to herein collectively as cells 12 andindividually as cell 12. Notably, while nineteen cells 12 areillustrated in FIG. 1 for clarity and ease of discussion, it will bereadily appreciated by one of ordinary skill in the art that thecellular communications network 10 may include any number of cells 12and, in most implementations, will include a relatively large number ofcells 12.

In this embodiment, the cells 12-1 through 12-19 are served bycorresponding base stations 14-1 through 14-19, which are generallyreferred to herein collectively as base stations 14 and individually asbase station 14. For LTE, the base stations 14 are typically enhancedNode Bs (eNBs) but may also include low power base stations (e.g., homeeNBs or femto base stations). Further, while in this embodiment each ofthe base stations 14 serves only one cell 12, one or more of the basestations 14 may alternatively serve multiple cells 12. For instance, inLTE, an eNB may serve multiple cells, or sectors. The base stations 14provide cellular communications services (e.g., voice and data services)to mobile terminals (MTs), such as a mobile terminal 16 located in thecell 12-1. While only one mobile terminal 16 is illustrated in FIG. 1,it will be readily appreciated by one of ordinary skill in the art thatthe cellular communications network 10 will typically serve hundreds,thousands, or even millions of mobile terminals 16.

As discussed below in detail, the base stations 14, or at least some ofthe base stations 14, provide selective RoHC for VoIP calls. In general,each of the base stations 14 has a finite amount of resources (i.e.,processing cycles and memory resources) that can be used for RoHC, wherethese resources are referred to herein as RoHC resources. The RoHCresources of each base station 14 are logically divided into afirst-come, first-serve RoHC resource pool and a selective RoHC resourcepool. The first-come, first serve RoHC resource pool includes an amountof RoHC resources that is sufficient to provide RoHC for a number(N_(FCFS)) of VoIP calls, and the selective RoHC resource pool includesan amount of RoHC resources that is sufficient to provide RoHC for anumber (N_(SELECTIVE)) of VoIP calls. Note that N_(FCFS) andN_(SELECTIVE) may vary among the base stations 14 depending on thefinite amount of RoHC resources of each of the base stations 14. In oneembodiment, N_(SELECTIVE) is in a range of 10% to 15% of the finiteamount of RoHC resources of the base station 14, whereas N_(FCFS) is theremainder of the finite amount of RoHC resources of the base station 14.Thus, in other words, N_(SELECTIVE) is in a range of 10% to 15% of atotal number of VoIP calls for which the finite amount of RoHC resourcescan provide RoHC, whereas N_(FCFS) is the remainder.

The base stations 14 provide selective RoHC for VoIP calls based on acoverage-based condition. More specifically, the base stations 14provide selective RoHC for VoIP calls such that the selective RoHCresources of the base stations 14 are only available for VoIP calls forwhich the coverage-based condition is satisfied. In one preferredembodiment, the coverage-based condition is a Signal to Interferenceplus Noise Ratio (SINR) that is less than a predefined threshold. Stillfurther, in one particular embodiment, the coverage-based condition isthe same condition used to trigger Transmit Time Interval (TTI)bundling. By reserving the selective RoHC resources for VoIP calls thatsatisfy the coverage-based condition, the base stations 14 ensure thatRoHC resources are available for VoIP calls that would most benefit fromthe cell coverage improvement provided by RoHC.

FIG. 2 is a flow chart that illustrates the operation of one of the basestations 14 of FIG. 1 to provide selective RoHC for a VoIP callaccording to one embodiment of the present disclosure. For thisdiscussion, the base station 14 is the base station 14-1, and the VoIPcall is a VoIP call either to or from the mobile terminal 16 located inthe cell 12-1 of the base station 14-1. The process begins when a DataRadio Bearer (DRB) for a VoIP call either to or from the mobile terminal16 is to be established. This may be when a VoIP call to or from themobile terminal 16 is initially set up or when there is an inter-cellhandover of the VoIP call to the base station 14-1.

When a DRB for the VoIP call is to be established, the base station 14-1determines whether RoHC resources are available in the first-come,first-serve RoHC resource pool of the base station 14-1 (step 100). Ifso, the base station 14-1 establishes a DRB for the VoIP call with RoHCenabled (step 102). Preferably, RoHC is enabled in both the uplink anddownlink directions. If there are no available RoHC resources in thefirst-come, first serve RoHC resource pool of the base station 14-1, thebase station 14-1 establishes a DRB for the VoIP call with RoHC disabled(step 104). Note that, after establishing the DRB with RoHC disabled,the base station 14-1 may optionally monitor the first-come, first-serveRoHC resource pool of the base station 14-1 to determine if RoHCresources subsequently become available and, if so, enable RoHC for theVoIP call.

After establishing the DRB for the VoIP call with RoHC disabled in step104, the base station 14-1 monitors a Radio Frequency (RF) parameter forthe DRB to determine when a predefined coverage-based condition issatisfied. More specifically, the base station 14-1 obtains the RFparameter for the DRB (step 106). The base station 14-1 then determineswhether the RF parameter satisfies the predefined coverage-basedcondition (step 108). In one preferred embodiment, the RF parameter is aSINR for the DRB, and the predefined coverage-based condition is acondition where the SINR is less than a predefined threshold. Further,in one preferred embodiment, the predefined coverage-based condition isthe same condition used to trigger TTI bundling (e.g., the same SINRthreshold used to trigger TTI bundling).

If the predefined coverage-based condition is not satisfied, the processreturns to step 106 and is repeated. Conversely, if the predefinedcoverage-based condition is satisfied, the base station 14-1 thendetermines whether there are available RoHC resources in either thefirst-come, first-serve RoHC resource pool or the selective RoHCresource pool of the base station 14-1 (step 110). If not, the processreturns to step 106 and is repeated such that RoHC may thereafter beenabled if the predefined coverage-based condition is satisfied and RoHCresources become available. If RoHC resources are available in eitherthe first-come, first-serve RoHC resource pool or the selective RoHCresource pool of the base station 14-1, the base station 14-1 enablesRoHC for the VoIP call (step 112). As discussed below, in one particularembodiment, the base station 14-1 enables RoHC for the VoIP call byperforming an intra-cell handover to a new DRB that has RoHC enabled.Using the process of FIG. 2, the base station 14-1 reserves theselective RoHC resource pool for those VoIP calls that would benefitmost by the cell coverage improvement provided by RoHC. Thus, theselective RoHC resource pool prevents starvation of RoHC resources forthose VoIP calls that would most benefit from RoHC, while thefirst-come, first-serve RoHC resource pool allows RoHC for all VoIPcalls as long as there are sufficient RoHC resources in the base station14-1.

As mentioned above, in one preferred embodiment, the RF parameter andthe predefined coverage-based condition are the same as those used totrigger TTI bundling. As such, before proceeding, a brief overview ofHybrid Automatic Repeat Request (HARQ) and TTI bundling is beneficial.In LTE as well as most other modern cellular communications standards, aHARQ transmission scheme is utilized. HARQ utilizes both forwarderror-correction coding and Automatic Repeat Request (ARQ) to enablesuccessful reception and decoding of transmissions under varying channelconditions. When using HARQ, the mobile terminal 16 requestsretransmission for erroneously received packets as illustrated in FIG.3A. TTI bundling is triggered under poor radio conditions in order toreduce overhead. Notably, TTI bundling is also referred to as subframebundling. Also, when TTI bundling is not enabled, HARQ operation isreferred to as normal HARQ operation. Typically, TTI bundling istriggered, or enabled, when the SINR falls below a predefined threshold.Currently, for LTE, the HARQ transmissions are in the sequenceRedundancy Version (RV) 0, RV2, RV3, RV1. As illustrated in FIG. 3B,when using TTI bundling, the TTIs for the initial HARQ transmission andone or more subsequent HARQ retransmissions are grouped, or bundled,into successive TTIs. In this manner, the base stations 14 are enabledto successfully receive and decode the transmission with reducedoverhead (i.e., without the mobile terminal 16 transmitting multipleNACKs) and with less latency.

FIG. 4 illustrates the operation of one of the base stations 14 toperform selective RoHC based on the same coverage-based condition usedto trigger TTI bundling according to one embodiment of the presentdisclosure. For this discussion, the base station 14 is the base station14-1. In this example, initially, both TTI bundling and RoHC aredisabled for a VoIP call either to or from the mobile terminal 16 (step200). As such, VoIP transmissions are transmitted over a DRB having bothTTI bundling and RoHC disabled (step 202). At some point during the VoIPcall, the base station 14-1 makes a decision to enable TTI bundling forthe VoIP call (step 204). More specifically, the base station 14-1monitors an RF parameter for the VoIP call. When the RF parametersatisfies a predefined condition for triggering TTI bundling, the basestation 14-1 makes the decision to enable TTI bundling. In one preferredembodiment, the RF parameter is SINR, and the predefined condition fortriggering TTI bundling is a condition that the SINR falls below apredefined threshold.

In response to the decision to enable TTI bundling, the base station14-1 performs a selective RoHC admission process in order to decidewhether RoHC resources are available (step 206). In general, the basestation 14-1 determines whether RoHC resources are available in eitherthe first-come, first-serve RoHC resource pool or the selective RoHCresource pool of the base station 14-1. In this example, the basestation 14-1 determines that RoHC resources are available. As such, thebase station 14-1 initiates an intra-cell handover to enable both TTIbundling and RoHC. Notably, in this embodiment, the decision on whetherto selectively enable RoHC for the VoIP call is piggy-backed on thedecision to enable TTI bundling.

For LTE, in order to perform the intra-cell handover, the base station14-1 first sends an RRCConnectionReconfigurationRequest message to themobile terminal 16 in order to request a new DRB for the VoIP callhaving both TTI bundling and RoHC enabled (step 208). From this point,the conventional LTE intra-cell handover procedure is performed.Specifically, the mobile terminal 16 sends a random access preamble tothe base station 14-1 (step 210). In response, the base station 14-1then returns a random access response to the mobile terminal 16 (step212). At that point, the mobile terminal 16 sends anRRCConnectionReconfigurationConfirm message to the base station 14-1confirming that both TTI bundling and RoHC are enabled for the new DRBfor the VoIP call (step 214). At this point, the intra-cell handover iscomplete. Using the intra-cell handover, the base station 14-1simultaneously enables both TTI bundling and RoHC for the VoIP call.Notably, in LTE, TTI bundling is only enabled in the uplink. However,RoHC is preferably enabled for the DRB in both the uplink and downlinkdirections.

Once the intra-cell handover is complete, the base station 14-1 updatesthe appropriate RoHC resource pool to indicate that the RoHC resourcesused for the new DRB are no longer available (step 216). Note that whilein FIG. 4 the appropriate RoHC resource pool is updated after theintra-cell handover has been completed, the base station 14-1 mayalternatively update the appropriate RoHC resource pool at any timebetween the decision made in step 206 and the completion of theintra-cell handover. For example, the base station 14-1 may update theappropriate RoHC resource pool after making the decision in step 206 andbefore sending the RRCConnectionReconfigurationRequest in step 208 inorder to reserve RoHC resources for the new DRB. In this case, if theintra-cell handover fails, the base station 14-1 updates the appropriateRoHC resource pool to release the RoHC resources that were reserved forthe new DRB. Lastly, VoIP transmissions for the VoIP call aretransmitted over the new DRB having both TTI bundling and RoHC enabled(step 218).

FIG. 5 is a flow chart that illustrates the operation of the basestation 14-1 of FIG. 4 to perform a selective RoHC admission processand, if RoHC is enabled, update the appropriate RoHC resource poolaccording to one embodiment of the present disclosure. Thus, in general,FIG. 5 illustrates steps 206 and 216 of FIG. 4 in more detail accordingto one embodiment of the present disclosure. Again, for this discussion,the base station 14 is the base station 14-1. However, this discussionis equally applicable to the other base stations 14. First, the basestation 14-1 determines whether an intra-cell handover has beentriggered to enable TTI bundling (step 300). More specifically, asdiscussed above, the base station 14-1 determines whether the RFparameter for the DRB for the VoIP call satisfies the predefinedcondition for triggering TTI bundling. Again, in one preferredembodiment, the RF parameter is SINR, and the predefined condition fortriggering TTI bundling is the condition that the SINR falls below apredefined threshold for triggering TTI bundling.

If an intra-cell handover has not been triggered to enable TTI bundling,the process returns to step 300 and waits until an intra-cell handoverhas been triggered to enable TTI bundling. Once an intra-cell handoverhas been triggered to enable TTI bundling, the base station 14-1determines whether RoHC resources are available in the first-come,first-serve RoHC resource pool of the base station 14-1 (step 302). Ifso, the base station 14-1 initiates an intra-cell handover of the VoIPcall to a new DRB with both TTI bundling and RoHC enabled (step 304).The base station 14-1 then updates the first-come, first-serve RoHCresource pool to reflect that the RoHC resources used for the new DRBare no longer available (step 306). For example, the base station 14-1may maintain a counter that is equal the number of VoIP calls that areutilizing RoHC resources from the first-come, first-serve RoHC resourcepool. So, if all of the RoHC resources in the first-come, first-serveRoHC resource pool are available, then the counter would be equal to 0.Conversely, if none of the RoHC resources in the first-come, first-serveRoHC resource pool are available, then the counter would be equal toN_(FCFS). Thus, in this example, the base station 14-1 updates thefirst-come, first-serve RoHC resource pool by increasing the counterby 1. When the RoHC resources are subsequently released, the counter isdecreased by 1.

Returning to step 302, if there are no available RoHC resources in thefirst-come, first-serve RoHC resource pool, the base station 14-1determines whether there are available RoHC resources in the selectiveRoHC resource pool (step 308). If not, the base station 14-1 initiatesan intra-cell handover of the VoIP call to a new DRB with TTI bundlingenabled and RoHC disabled (step 310). Notably, if step 310 is triggeredoften, allocation of the RoHC resources of the base station 14-1 to thefirst-come, first-serve RoHC resource pool and the selective RoHCresource pool may be rebalanced in order to allocate more RoHC resourcesto the selective RoHC resource pool. This re-balancing may be performedprogrammatically by the base station 14-1 in response to the basestation 14-1 detecting that step 310 is performed often (e.g., for atleast a predefined threshold number or percentage of intra-cellhandovers triggered to enable TTI bundling). Alternatively, there-balancing may be performed manually by an operator of the basestation 14-1.

Returning to step 308, if RoHC resources are available in the selectiveRoHC resource pool, the base station 14-1 initiates an intra-cellhandover of the VoIP call to a new DRB with both TTI bundling and RoHCenabled (step 312). The base station 14-1 then updates the selectiveRoHC resource pool to reflect that the RoHC resources used for the newDRB are no longer available (step 314). For example, the base station14-1 may maintain a counter that is equal the number of VoIP calls thatare utilizing RoHC resources from the selective RoHC resource pool. So,if all of the RoHC resources in the selective RoHC resource pool areavailable, then the counter would be equal to 0. Conversely, if none ofthe RoHC resources in the selective RoHC resource pool are available,then the counter would be equal to N_(SELECTIVE). Thus, in this example,the base station 14-1 updates the selective RoHC resource pool byincreasing the counter by 1. When the RoHC resources are subsequentlyreleased, the counter is decreased by 1.

FIG. 6 is a block diagram of one of the base stations 14 of FIG. 1according to one embodiment of the present disclosure. The base station14 includes a transceiver subsystem 18 and a processing subsystem 20.The transceiver subsystem 18 generally includes analog and, in someembodiments, digital components for wirelessly sending and receivingmessages to and from the mobile terminals 16 in the cellularcommunications network 10. In particular embodiments, the transceiversubsystem 18 may represent or include a radio-frequency (RF)transceiver, or a separate RF transmitter and receiver, capable oftransmitting messages and/or other suitable information wirelessly tothe mobile terminal 16.

The processing subsystem 20 is implemented in hardware or a combinationof hardware and software. Among other things, the processing subsystem20 performs selective RoHC as described herein. In particularembodiments, the processing subsystem 20 may comprise, for example, oneor several general-purpose or special-purpose microprocessors or othermicrocontrollers programmed with suitable software and/or firmware tocarry out some or all of the functionality of the base station 14described herein. In addition or alternatively, the processing subsystem20 may comprise various digital hardware blocks (e.g., one or moreApplication Specific Integrated Circuits (ASICs), one or moreoff-the-shelf digital and analog hardware components, or a combinationthereof) configured to carry out some or all of the functionality of thebase station 14 described herein. Additionally, in particularembodiments, the above described functionality of base station 14 may beimplemented, in whole or in part, by the processing subsystem 20executing software or other instructions stored on a non-transitorycomputer-readable medium, such as random access memory (RAM), read onlymemory (ROM), a magnetic storage device, an optical storage device, orany other suitable type of data storage components.

FIG. 7 is a block diagram of the mobile terminal 16 of FIG. 1 accordingto one embodiment of the present disclosure. The mobile terminal 16includes a transceiver subsystem 22 and a processing subsystem 24. Thetransceiver subsystem 22 generally includes analog and, in someembodiments, digital components for wirelessly sending and receivingmessages to and from the base stations 14 in the cellular communicationsnetwork 10. In particular embodiments, the transceiver subsystem 22 mayrepresent or include an RF transceiver, or a separate RF transmitter andreceiver, capable of transmitting messages and/or other suitableinformation wirelessly to the base stations 14.

The processing subsystem 24 is implemented in hardware or a combinationof hardware and software. In general, the processing subsystem 24enables the mobile terminal 16 to perform the functions of the mobileterminal 16 described herein. In particular embodiments, the processingsubsystem 24 may comprise, for example, one or several general-purposeor special-purpose microprocessors or other microcontrollers programmedwith suitable software and/or firmware to carry out some or all of thefunctionality of the mobile terminal 16 described herein. In addition oralternatively, the processing subsystem 24 may comprise various digitalhardware blocks (e.g., one or more ASICs, one or more off-the-shelfdigital and analog hardware components, or a combination thereof)configured to carry out some or all of the functionality of the mobileterminal 16 described herein. Additionally, in particular embodiments,the above described functionality of the mobile terminal 16 may beimplemented, in whole or in part, by the processing subsystem 24executing software or other instructions stored on a non-transitorycomputer-readable medium, such as RAM, ROM, a magnetic storage device,an optical storage device, or any other suitable type of data storagecomponents.

The following acronyms are used throughout this disclosure.

ARQ Automatic Repeat Request

ASIC Application Specific Integrated Circuit

DRB Data Radio Bearer

eNB Enhanced Node B

HARQ Hybrid Automatic Repeat Request

HO Handover

IP Internet Protocol

LTE Long Term Evolution

MT Mobile Terminal

RAM Random Access Memory

RF Radio Frequency

RoHC Robust Header Compression

ROM Read Only Memory

RV Redundancy Version

SINR Signal to Interference plus Noise Ratio

TTI Transmit Time Interval

VoIP Voice over Internet Protocol

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A method of operation of a base station in acellular communications network, comprising: establishing a data radiobearer between the base station and a mobile terminal for a VoIP call;determining that a radio frequency parameter for the data radio bearersatisfies a predefined coverage-based condition; and in response todetermining that the radio frequency parameter for the data radio bearersatisfies the predefined coverage-based condition, enabling RoHC for theVoIP call.
 2. The method of claim 1 wherein enabling RoHC for the VoIPcall comprises performing an intra-cell handover of the VoIP call fromthe data radio bearer to a new data radio bearer that has RoHC enabled.3. The method of claim 2 further comprising: determining whether thebase station has available RoHC resources; and wherein enabling RoHC forthe VoIP call comprises enabling RoHC for the VoIP call if the basestation has available RoHC resources.
 4. The method of claim 1 whereinthe radio frequency parameter is a SINR parameter, and the predefinedcoverage-based condition is a predefined SINR threshold for triggeringTTI bundling.
 5. The method of claim 4 wherein: determining that theradio frequency parameter for the data radio bearer satisfies thepredefined coverage-based condition comprises determining that the SINRparameter is less than the predefined SINR threshold for TTI bundling;and enabling RoHC for the VoIP call comprises enabling both TTI bundlingand RoHC for the VoIP call in response to determining that the SINRparameter is less than the predefined SINR threshold for TTI bundling.6. The method of claim 5 further comprising: determining whether thebase station has available RoHC resources; wherein enabling both TTIbundling and RoHC for the VoIP call comprises enabling both TTI bundlingand RoHC for the VoIP call if the base station has available RoHCresources.
 7. The method of claim 4 wherein enabling both TTI bundlingand RoHC for the VoIP call comprises simultaneously enabling both TTIbundling and RoHC for the VoIP call.
 8. The method of claim 7 whereinsimultaneously enabling both TTI bundling and RoHC for the VoIP callcomprises performing an intra-cell handover of the VoIP call from thedata radio bearer to a new data radio bearer that has both TTI bundlingand RoHC enabled.
 9. The method of claim 7 further comprising:determining whether the base station has available RoHC resources;wherein simultaneously enabling both TTI bundling and RoHC for the VoIPcall comprises performing an intra-cell handover of the VoIP call fromthe data radio bearer to a new data radio bearer that has both TTIbundling and RoHC enabled if the base station has available RoHCresources.
 10. The method of claim 9 wherein the base station has afinite amount of RoHC resources that are logically divided into afirst-come, first-serve RoHC resource pool and a selective RoHC resourcepool, and determining whether the base station has available RoHCresources comprises: determining whether there are available RoHCresources in the first-come, first-serve RoHC resource pool; and ifthere are no available resources in the first-come, first-serve RoHCresource pool, determining whether there are available RoHC resources inthe selective RoHC resource pool.
 11. A base station in a cellularcommunications network, comprising: a transceiver subsystem; and aprocessing subsystem associated with the transceiver subsystemconfigured to: establish, via the transceiver subsystem, a data radiobearer between the base station and a mobile terminal for a VoIP call;determine that a radio frequency parameter for the data radio bearersatisfies a predefined coverage-based condition; and in response todetermining that the radio frequency parameter for the data radio bearersatisfies the predefined coverage-based condition, enable RoHC for theVoIP call.
 12. The base station of claim 11 wherein, in order to enableRoHC for the VoIP call, the processing subsystem is further configuredto perform an intra-cell handover of the VoIP call from the data radiobearer to a new data radio bearer that has RoHC enabled.
 13. The basestation of claim 12 wherein the processing subsystem is furtherconfigured to: determine whether the base station has available RoHCresources; and enable RoHC for the VoIP call if the base station hasavailable RoHC resources.
 14. The base station of claim 11 wherein theradio frequency parameter is a SINR parameter, and the predefinedcoverage-based condition is a predefined SINR threshold for triggeringTTI bundling.
 15. The base station of claim 14 wherein the processingsubsystem is further configured to: determine that the SINR parameter isless than the predefined SINR threshold for TTI bundling; and enableboth TTI bundling and RoHC for the VoIP call in response to determiningthat the SINR parameter is less than the predefined SINR threshold forTTI bundling.
 16. The base station of claim 15 wherein the processingsubsystem is further configured to: determine whether the base stationhas available RoHC resources; and enable both TTI bundling and RoHC forthe VoIP call if the base station has available RoHC resources.
 17. Thebase station of claim 14 wherein the processing subsystem is furtherconfigured to simultaneously enable both TTI bundling and RoHC for theVoIP call if the base station has available RoHC resources.
 18. The basestation of claim 17 wherein the processing subsystem is furtherconfigured to simultaneously enabling both TTI bundling and RoHC for theVoIP call via an intra-cell handover of the VoIP call from the dataradio bearer to a new data radio bearer that has both TTI bundling andRoHC enabled.
 19. The base station of claim 17 wherein the processingsubsystem is further configured to: determine whether the base stationhas available RoHC resources; and simultaneously enable both TTIbundling and RoHC for the VoIP call via the intra-cell handover of theVoIP call from the data radio bearer to the new data radio bearer thathas both TTI bundling and RoHC enabled if the base station has availableRoHC resources.
 20. The base station of claim 19 wherein the processingsubsystem comprises a finite amount of RoHC resources that are logicallydivided into a first-come, first-serve RoHC resource pool and aselective RoHC resource pool, and, in order to determine whether theprocessing subsystem has available RoHC resources, the processingsubsystem is further configured to: determine whether there areavailable RoHC resources in the first-come, first-serve RoHC resourcepool; and if there are no available resources in the first-come,first-serve RoHC resource pool, determine whether there are availableRoHC resources in the selective RoHC resource pool.
 21. A method ofoperation of a mobile terminal in a cellular communications network,comprising: communicating, for a VoIP call, over a data radio bearerbetween a base station and the mobile terminal for the VoIP call;receiving an intra-cell handover request from the base station for anintra-cell handover from the data radio bearer to a new data radiobearer between the base station and the mobile terminal for the VoIPcall with RoHC enabled; communicating with the base station to performthe intra-cell handover from the data radio bearer to the new data radiobearer for the VoIP call with RoHC enabled; and communicating, for theVoIP call, over the new data radio bearer.
 22. The method of claim 21wherein receiving the intra-cell handover request comprises receivingthe intra-cell handover request from the base station for an intra-cellhandover from the data radio bearer to the new data radio bearer betweenthe base station and the mobile terminal for the VoIP call with both TTIbundling and RoHC enabled.